Traffic is the everlasting nightmare for every metropolitan driver, and it is no truer when trying to find a parking place in any major city. To encounter this problem, a vehicle with ability to turn in tight space had been proposed. As the advance of motor and its control technology, some advanced vehicles, especially the rectangle four-wheeled vehicles, are configured with four wheel steering mechanism which cooperates with a motor-driven steering switching mechanism to enable two front wheels of the vehicle to be toe-in and two rear wheels to be toe-out so as to enable the vehicle to turn about in tight space by the help of a corresponding power system. Such vehicles can have good maneuverability and steering that is easy to park and turn around. However, mechanisms, components and controls for enabling a rectangle four-wheeled vehicle to turn-in-spot in tight space are quite complicated, bulky and heavy, moreover, it has adverse affects on wheel and chassis alignment. Particularly, for those smaller size automobiles running in downtown area with quite small internal spaces and the weight thereof are preferred to be reduced for fuel efficiency, the aforesaid four wheel steering mechanism enabling turn-in-spot must be simplified. In addition, the operations of negotiating a turn and making a U-turn in tight space of the rectangle four-wheeled vehicle using the aforesaid four wheel steering are independent to each other, which makes the operations of the mechanism even more complicate.
A three-wheeled vehicle with one front wheel and two rear wheels is much simpler at system complexity than rectangle four-wheeled vehicle (only two wheels need mechanism control), but the three-wheeled vehicle must enable the two rear wheels to toe-out while steering the front wheel to turn at 90 degrees for enabling the three-wheeled vehicle to turn-in-spot in tight space. Furthermore, without two rear wheels to toe-out, since the forgoing turn is centering about the intersection of the rear wheel shaft and the longitudinal shaft of the vehicle frame, the minimum turning radius is the front and rear wheelbase. Compared with the abovementioned four-wheeled vehicle with ability to turn in tight space, the turning radius of the three-wheeled vehicle is twice as large as that of the four-wheeled vehicle that the three-wheeled vehicle requires large space for turning.
As to patents of a rhombus four-wheeled vehicle, the representative patents include U.S. Pat. No. 1,262,806, entitled “Rolling Chair”, U.S. Pat. No. 3,828,876, entitled “Motor Vehicle Having Wheels in a Diamond pattern”, U.S. Pat. No. 4,313,511, entitled “Land Vehicle”, U.S. Pat. No. 4,775,021, entitled “Automotive Vehicle Having Four Wheels in a Rhomboidal Configuration”, and so on. The structure and shortcomings of the conventional rhombus four-wheel vehicles are described hereinafter in accordance with the technical means of the above patents.
Referring to FIG. 1, U.S. Pat. No. 1,262,806, entitled “Rolling Chair”, is a pioneer US patent of a rhombus four-wheeled vehicle. The two side wheels 8 are coaxial without speed difference and are driven by an electric motor, whereas the front wheel 10 can be steered manually and the rear wheel 11 can roll freely. The shortcomings of the aforesaid patent are that the driving forces of the two side wheels 8 will interfere with each other while negotiating a turn that the four-wheeled vehicle fails to perform a U-turn in tight space.
Referring to FIG. 2, U.S. Pat. No. 3,828,876, entitled “Motor Vehicle Having Wheels in a Diamond Pattern” disclosed a vehicle having a front wheel R1 as a steering wheel and two side wheels R2, R3 employed as driving wheels, wherein the axis of the rear wheel R4 is arranged to parallel to the axis of the side wheels R2, R3 at all time while the rear wheel R4 is maintained to roll freely without turning. The shortcomings of the aforesaid patent are that: as the axles of the rear three wheels R2, R3, R4 are maintained to parallel to each other at all time while being arranged to perpendicular to the longitudinal shaft of the vehicle frame, the lateral force of the rear three wheels R2, R3, R4 exerting on the ground can interfere with each other such that the vehicle fails to perform a U-turn in tight space.
Please to FIG. 3, which is a vehicle disclosed in U.S. Pat. No. 4,313,511, entitled “Land Vehicle”. In the vehicle of FIG. 3, either the front wheel 19 or rear wheel 21 is employed as a steering wheel through mechanism control while disabling another for steering, and suspension systems 101, 103 of the two side wheels 24, 27 are controlled through mechanism control to incline inwardly during steering for simultaneously controlling two side wheels 24, 27 to turn with the steering wheel (i.e. the front wheel 19 or the rear wheel 21). The shortcomings of the aforesaid patent are that although the multiple-wheel control of the aforesaid patent can enhance maneuverability, it is complicated and fails to enable a vehicle to perform a U-turn in tight space.
Please refer to FIG. 4, which is a vehicle disclosed in U.S. Pat. No. 4,775,021, entitled “Automotive Vehicle Having Four Wheels in a Rhomboidal Configuration”. The vehicle of FIG. 4 has four independent-suspended and independent-driven wheels 2˜5, wherein the front and rear wheels 4, 5 are respectively suspended by an L-shaped arm, and a steering arm is additionally configured to cooperate with a steering rod extending through the vehicle frame for enabling the front and rear wheels 4, 5 to turn simultaneously and opposite to each other, thereby controlling over-steering. The shortcomings of the aforesaid patent are that it requires precise technology to control a multi-wheeled drive system and the vehicle fails to perform a U-turn in tight space.